This invention relates to vibration dampening devices and more specifically to a conductor galloping control device and a method for installation.
Historically, there has been increased emphasis, worldwide, to develop practical solutions to the problem of vibration on overhead lines. There are several types of vibrations of overhead conductors, including galloping and aeolean vibration. Galloping vibration refers to a high amplitude low frequency vibration differing from an aeolean vibration which is defined as a low amplitude high frequency vibration. A number of devices, methods and techniques which have demonstrated successful suppression of vibration motion continue to be under close scrutiny by the electric power industry.
Galloping of overhead lines is associated with freezing rain, wet snow or frost which forms a deposit on conductors and changes their profile shape. With a moderate wind passing over this asymmetrical profile, the conductor may move in the vertical, torsional or horizontal direction initiating the galloping motion. The addition of devices that modify the position of ice accretion on the conductor so that the iced-conductor will present a changeable xe2x80x9cangle of attackxe2x80x9d to the wind direction have been developed to alleviate the gallop effect. By directly changing the angle of attack to the wind, one of the most active factors in a galloping system, the aerodynamic forces will not behave in such a way that upward velocity increases the vertical force and that downward velocity decreases the vertical force. The classic rise and fall effect that produces galloping is not allowed, thus self-sustained oscillations can be avoided.
Since 1979, extensive field experience has been gathered on an add-on helical straking device for the control of galloping; namely the air flow spoiler. In the past, spoilers were manufactured from nonmetallic rods of various diameters with an overall length of approximately 4.3 meters. Each end of the spoiler has a factory formed helical xe2x80x9cgrippingxe2x80x9d section designed to fit tightly over a narrow range of conductor diameters. The straight section between the end gripping sections is field-wrapped tightly around the conductor twice to form a xe2x80x9cspoilingxe2x80x9d section with two helical turns.
U.S. Pat. No. 4,620,059, to Sherman, discloses a device for suppressing wind induced motion in aerial cables and a method for installing the device. The device comprises a fourteen foot straight rod with helical gripping ends on the distal and proximal end of the straight center portion. The distal end section is made up of a double helix and the proximal end includes a triple helix where the helical twist nearest the straight section has a larger inside diameter for installation purposes. Sherman also discloses a method for installing the device. Installation involves the hooking of the triple helix side of the device to the cable and sliding the device down the cable until the double helix side is in front of the installer. The installer then wraps the double helix side around the cable. Once the double helix end is secure, the installer then wraps the straight center portion around the cable twice. Finally, the installer moves to the triple helix end and wraps the triple helix around the cable completing installation.
The Sherman design is disadvantageous at least because of its overall length, initial straight portion and installation method. The overall length of the Sherman device is fourteen feet. At fourteen feet, the air spoiler is cumbersome for a single installer due to the flexible nature of the material used in manufacturing the rod. Furthermore, the manual twisting of the straight center portion around the cable during installation presents opportunity for injury because the straight rod must be manually twisted to conform to the cable. In addition, the installer must move a lift device, such as a bucket lift, from one end of the device to the other during installation to wrap each gripping end around the cable.
This invention is a conductor galloping control device for aerial conductors. The device has a middle disturbance section, a first gripping section and a second gripping section. The second gripping section is designed to facilitate installation. The middle disturbance section has preformed helixes with the same pitch length. All the turns in each section have the same helix diameter, but have different numbers of helical turns and differing pitch lengths. Pitch length is defined as the distance between a point on one helical turn and the corresponding point on the next helical turn.
It is a primary object of this invention to provide the aerial cable industry with a conductor galloping control device that is easier to install. It is a further object of this invention to provide a conductor galloping control device that is safer to install. An additional object of this invention is to provide a method for installing a conductor galloping control device by one person without having to move a lifting device, such as a bucket lift, during aerial installation. A farther object of this invention is to reduce the cost for the prevention of galloping by lowering the manufacturing costs due to the reduced length of the device. Still further objects and advantages will become apparent from a consideration of the ensuing description and drawings.